At 3:52 a.m. yesterday, a middle-aged man walked into the Reliance Co-operative Bank at 15 Dunster St. and passed a note to one of the tellors. The note read: "Just a hold-up, don't he alarmed, give me all your $5's, $10's and $20's." She handed him $1,875, which he stuffed into his pockets.

According to Sgt. Leo F. Davenport of the Cambridge Police, the bandit left on foot in an "old, green raincoat similar to what you'd see a professor wearing." He then walked up Dunster St. across Massachusetts Ave. to the MBTA, leaving a trail of bills behind him.

Sgt. Davenport retrieved the money and returned over $500 to the bank. But the robber got away.

The unassuming and effective modus operandi was similar to that employed in the stickup of the Cambridge Federal Savings and Loan Association last March 8. In both cases the bandit was a short, stocky man around 50 years old. Both banks are set away from the busy Square area, and both robberies took place around 9 a.m. In the Cambridge Federal hold-up the bandit made off with $2700.

Stuart M. Mabie, treasurer of the Reliance Co-operative, said it was the first and only robbery in the Bank's 75 years